Treatment of synthetic linear polyamide threads



. Patented July 26, 1949 TREATMENT OF sYNTnETIc POLYAMIDE THREAD Joseph Elmer Waltz, Wilmington, Del., assignor to E. I. du Pont de Ncmours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application April 12, 1948, Serial No. 861,910

' 3 Claims. 1

This invention relates to improved plied structures, particularly sewing threads composed of synthetic linear polyamide filaments.

The invention will be described with particular reference to sewing threads composed of polyhexamethylene adipamide filaments although it will be understood that within its broad scope, the invention pertains to the various other synthetic linear polyamides.

Sewing threads composed of polyhexamethyl- Y ene adipamide filaments, satisfactory in all respects, have not previously been developed. Such sewing threads are used on conventional sewing machines which develop relatively high temperatures in operation and the melting point of polyhexamethylene adipamide sewing threads is not high enough to withstand such temperatures to the desired degree of satisfaction. Furthermore, the elongation of such nylon sewing threads, which is already high at ordinary temperatures, increases further at the temperatures prevailing during the sewing machine operation to a point which greatly exceeds that which conventional sewing machines can handle.

An object of this invention is to produce improved structures plied from synthetic linear polyamide yarn. A further object of the invention relates to sewing thread composed of synthetic linear polyamide yarn and characterized by high tenacity, low elongation and a relatively high melting point. Other objects will be apparent hereinafter.

The objects of the invention are accomplished in general by treating oriented, synthetic linear polyamide sewing thread with formaldehyde, hot-stretching the treated thread to a point where it has a low residual elongation and permitting the stretched thread to cool at least 5% of the hot-stretching temperature above 0 C.

i while maintaining the structure in its stretched condition, after which the stretching force may be released.

'A sewing thread is normally a plied yam. A typical example is one made of three ends of oriented 210 denier, 34 filament, 21-8 twist nylon yarn, the ply twist being-10.6-Z. Such a standard nylon sewing thread will conventionally have a tenacity of 7.0'grams per denier, an elongation of 21% and a zero strength temperature of 267 C. It will not work very well on high speed sew ing machines (3,500 stitches per minute), especially with heavy fabrics. The stitching will be non-uniform due to the high elongation of the yarn, and the heat of friction of the needle'will cause the yarn to. melt. If such a thread is treated with formaldehyde without being hotstretched, the zero strength temperature can be raised beyond 300 0., which is quite satisfactory, but there is a considerable rise in elongation and there may be some impairment of tenacity. For example, the typical thread described above will. after the formaldehyde treatment, have a tenacity of 6.6 grams per denier and an elongation of 27%. The continuity of the sewing and the uniformity of the stitches will by no means be commercial for a good many types of sewing.

It has now been found that if such a thread is, treated with formaldehyde and then hotstretched in accordance with this invention, the thread will generally have an increased tenacity, e. g. about 7.7 grams per denier, an elongation of 12.5% and a zero strength temperature higher than 320 C. That the effect is not due solely to the hot-stretching is proved by the fact that such a thread, hot-stretched but not treated with formaldehyde, will have a tenacity of 1.8 grams per denier, an elongation of 12.4%, but a zero strength temperature of only 267 C. Similarly, a thread which is so hot-stretched and then treated with formaldehyde will have characteristics rather closely approaching those of a thread which was formaldehyde treated without hotstretching. The sewing thread of this invention is by far the most satisfactory nylon sewing thread developed and performs quite well in sev- Example I A 680 denier sewing thread was plied with a twist of 10.6 2 turns per inch from three ends of 210 denier, 34 filament nylon yarn melt spun from polyhexamethylene adipamide and having 21' turns per inch 8 twist. The original thread had a tenacity of 7.0 grams per denier, an elongation of 20.8% and a zero strength temperature of 266 C.

A 150 yard skein of the above thread was soaked for fifteen and one half hours at 30 C.

in 220 milliliters of an aqueous solution containing 37% formaldehyde in which was dissolved 0.5 gram of maleic acid. The sewing thread was conditioned on a swift for twenty-four hours at 50% relative humidity and 78 F. and then hot- 56 stretched through a 40-inch brass slot heated to 213 0., using a stretch ratio of 1.21 and a windup speed of 50 feet per minute. The yarn was held in the stretched condition until the temperature had dropped at least 10.6" C. The resulting thread had a denier of 610, a tenacity of 6.9 grams per denier, a break elongation of 12.3% and a zero strength temperature of greater than 328 6.. and contained 0.1% combined formaldehyde.

' Emmple II The sewing thread subjected to treatment was the same as that used for Example I.

A 150 yard skein of the sewing thread was soaked for sixteen hours at 30 C. in a solution of 220 milliliters ofan aqueous solution containing 37% formaldehyde and 0.5 gram of oxalic acid (K202003110). After conditioning and hot-stretching the thread and permitting it to cool while maintaining stretch in exactly the same manner as in Example I (above), the thread had a zero strength temperature of 318 C. and a com bined formaldehyde content of 0.1%.

Example III The sewing thread subjected to treatment was the same as that used for Example I.

A 150 yard skein of the sewing thread was soaked for thirty minutes in a solution of 5 grams of catechol (to improve durability of the finished thread upon exposure to sunlight) and 3 grams of oxalic acid in 200 milliliters of an aqueous solution containing 37% formaldehyde. The thread was then conditioned on a swift for twenty-four hours at 50% relative humidity and 78 F. and hot-stretchedthrough a 40-inch brass slot heated to 2l,z c.-using a stretch ratio of 1.19 and a windup of-50 feet per minute. The thread was then, permitted to cool at least 5% of its mammum temperature during stretching. while maintaining the stretch. The resulting physical properties shown in the table below:

Untreated Untreated Example Sewin Thread Hot- Thread Stretched m Denis 680 590 642 Tenacity, grams per I I dmiuifnnii. 7.0 7. 6 7. 6 Break on on,

cults. f i f 20. 8 12. 2 ll. 3 Zero amperama ogram C 266 266 320 Example IV The sewing thread of Example I was soaked in formaldehyde (880 milliliters containing 3.0 grams of maleic acid) as in Example I except that the time of soaking was sixteen hours. The conditioning was carried out similarly to that of Example 1 except that the temperature of conditioning was 65 C. and the time was twenty-five hours. flot-stretcbing was carried out similarly to the. procedure of Example I with the exception that the hot-stretching ratio was 1.23 and the windup speed was 150 feet per minute. The resulting thread had a denier of 607, a tenacity of 7.0 grams per denier and an elongation of 13.1%

with zero strength temperature above 320 0.

While commercial formalin, i. e. a 37% aqueous solution of formaldehyde, is preferred as the treating agent because of its low cost and ready availability, paraform, trloxymethylene and compounds which will readily yield formaldehyde may be used in lieu thereof. The concentration of formaldehyde is not critical. While a 37% aqueous solution of formaldehyde is preferred since 4. it is readily available as a commercial article, concentrations otha' than 37% are satisfactory, e. g. concentrations in water of 5% to 37% by weight of formaldehyde.

Although a specific sewing thread has been referred to in the above examples, it will be understood that the invention may be employed on any of the commercial nylon sewing thread structures. Sewing threads are plied from two or more yarns and it is preferred that the treatment of the invention be carried out on the plied structure rather than on the individual plies or the elementary yarns making up a ply. The ply twist may vary within wide'limits, depending on the exact type of sewing thread desired, but the ply twist will preferably be between 8 and 20 turns and opposite the yarn twist. The yarn twist may likewise vary considerably, being preferably between 10 and 20 turns with the yarn twist being generally 8 twist and the ply twist being generally 2 twist. Reference is made to Sommaripa Patent No. 2,251,962, issued August 12, 1941, which discloses suitable twist constructions for sewing threads plied from two or more synthetic linear polyamide yarns and useful for the production of sewing threads treated in accordance with the present invention.

The manner of treating the thread with the formaldehyde is not critical. The thread may be immersed in the solution as a skein or a spool, or any other convenient package. Alternatively, the running yarn may be passed through a formaldehyde solution, or the solution may be showered on to the yarn in some convenient way. It is preferred to use catalysts with the formaldehyde treatment so as to facilitate the combination of formaldehyde with synthetic linear polyamide. Catalysts which may be used. include organic polybasic acids having an ionization constant for the first hydrogen of between 1 X 10- and 1 X Illfor example, maleic, oxalic and phthalic, having, respectively, ionization constants for the first hydrogen of 1.5x10-=, 3.8X10- and 126x10 Inorganic acids, insofar as they satisfy these ionization requirements, may also be used. While the catalyst concentration is preferably about 0.25% by weight of the formaldehyde solution used, concentrations of 0.1% to 2.0% of catalyst based on the weight of the formaldehyde solution will operate satisfactorily.

The time of treatment with the formaldehyde is not critical. Depending upon such things as the type of package and the denier of the thread, it may vary from five minutes to thirty minutes. It has been found that thirty minutes is adequate under all reasonable circumstances.

The combined formaldehyde content of the final hot-stretched yarn may be from 0.01% to 1.0% and is preferably from 0.10% to 0.30%.

The conditioning of the treated thread prior to hot-stretching should be carefully controlled. The efliciency of hot-stretching depends on the moisture content of the thread and effective hotstretching cannot be carried out on a really wet thread. The moisture should be reduced to 5%. or preferably 3% or less. On the other hand, if the conditioning is carried out under such circumstances that cross-linking of the polyamide by the formaldehyde takes place, effective hotstretching is prevented. It has been found that the moisture should be removed at a temperature below that which promotes cross-linking (e. g. preferably below 65 C. and certainly below C). This conditioning can be carried out, for example, in lessthan twenty-four hours at 65 0. or less than forty hours at 30" c. to obtain a thread which, prior to hot-stretching, contains at least 0.2% and preferably 0.66% to 2.0%

formaldehyde based on the weight of the nylon.

In practicing the invention, the final sewing thread should have an elongation of 14)% or less. This can readily be accomplished by hot-stretching to the limit of elongation prior to breaking of the filaments, the sewing thread after the required degree of cooling before release of stretch exhibiting the desired elongation. It is generally preferred to ply the sewing thread from nylon yarns having an elongation of 30% or less in order that the stretching required for the hotstretching step be of a somewhat low order of magnitude. By utilizing nylon yarns which have been highly drawn, 1. e. which have an elongation of 30% or less, the stretching required during the hot-stretching of the sewing thread may be effected with a relatively low amount of stretch, for example 40% or less. It is convenient to stretch the sewing thread in the hotstretching step to its practical limit of elongation which is the maximum elongation tolerated without filament breakage. The preferred range of stretching in the hot-stretching step is to of the straight length of the sewing thread before stretching.

The hot-stretching is carried out by heating the so-treated sewing thread to a temperature of 190 to 215 C., stretching, and holding the yarn so stretched until the temperature has dropped at least 5% below the maximum yarn temperature above 0 C. reached duringstretching. The operation can be carried out conveniently by passing the yarn between two positively driven yarn stretching devicesas is well known, the thread moving through a heated zone. The thread may readily be permitted to reach the desired temperature for the hot-stretching operation by passing it between the two sets of stretching rollers through a slot in a heater which may be heated by an electrical resistance element or by a vapor such as steam. The thread very quickly reaches the temperature of the medium through which it passes and may, if desired, be heated somewhat above the temperature at which stretching takes place. The yarn may readily be cooled by permitting it to pass around the second stretching roller a number of times so that the thread may .be exposed to the air long enough to cool it to the desired extent. Generally speaking, although the hot-stretching temperature is within the range 190 to 215 C., the hot-stretching may take place between 190 C. and the temperature at which melting of the nylon takes place. While it is sufilcient to cool the hot-stretched plied thread at least 5% of the temperature above 0 C. at which the thread is hot-stretched while maintaining the yarn in the stretched condition, increasingly more beneficial results are obtained if the cooling is substantially greater than 5%, e. g. 10% to 40%, of the degrees of temperature above 0 C. at which the hot-stretching is carried out. In referring to the temperature of hot-stretching. the maximum temperature reached in stretching is the point of reference with respect to the subsequent cooling. Thus, where a temperature of 200 C., for example, is the maximum temperature at which hot-stretching of the thread takes place, the thread is preferably cooled down to 180 C. or below and preferably down to 150 C. or lower while maintaining the thread with at least the same degree of stretch imparted consisting essentially of bifunctional molecules number of carbon atoms separating the amide during the hot-stretching operation. If desired, the thread may be passed through molten Wood's metal instead of through a heated slot, or any other suitable means may be utilized for heating the yarn to eflect the hot-stretching. vHotstretching may be effected in stages if desired, in which event the maximum temperature at which stretching has been eflected will be the point of reference for the subsequent cooling of the yarn.

will not support the weight. This point is taken as the zero strength temperature.

The synthetic linear polyamides generally disclosed in Carothers Patents Nos. 2,071,250, 2,071,253 and 2,130,948 may be utilized in the production of yarns plied into the sewing thread which is treated by the procedure of this invention. The polyamides of this kind, generally speaking, comprise the reaction product of linear polymer-forming compositions containing amideforming groups, for example reacting material each containing two reactive groups which are complementary to reactive groups in other molecules and which include complementary amideforming groups. These polyamides can be obtained by 'the methods given in the above mentioned patents and by other methods, for example by self-polymerization of a monoaminomonocarboxylic acid, by reacting a diamine with a dibasic carboxylic acid in substantially equimolecular amounts, it being understood that reference herein to the amino acids, diamines, dibaslc carboxyllc acids and amino alcohols is intended to include the equivalent amide-forming derivatives of these reactants. The preferred polyamides obtained from these reactants have an intrinsic viscosity of at least 0.4 and a unit length of at least '7, where unit le h is defined as in U. S. Patents Nos. 2,071,253 and 2,130,948. The average groups in these polyamides is at least two.

These linear polyamides include also polymers, as for instance the polyester-amides, obtained by admixture of other linear polymer-forming reactants, as for instance glycol-dibasic acid mixtures or hydroxyacids, with the mentioned polyamide-forming reactants.

Both the-simple and modified linear-polyamides contain the recurring amide groups a x I ,ll N Q.

in which X- is oxygen or sulfur and R is hydrogen or a monovalent hydrocarbon radical, as an integral part of the main chain of atoms in the polymer. On hydrolysis with hydrochloric acid, the amino acid polymers yield the amino acid hydrochloride, the diamin'e-dibasic acid polymers yield the diamine hydrochloride and the dibasic carboxylic acid,'and the amino alcohol-dibasic acid polymers yield the amino alcohol hydrochloride and the .dibasic carboxylic acid.

The polyamides used for the preparation of the yarns or which the sewing thread is composed should be or sulllciently high molecular weight to have an intrinsic viscosity 01' at least 0.4 (as defined in U. 8. Patent No. 2,130,948) to insure the formation of tough fibers. This means that the polyamides used are those prepared from polymer-forming reactants containing complementary polymer-forming groups in substantially equimolecular amounts. Thus, 11' a polyamide of the diamine-dlbasic carboxylic acid type is used, the diamine and dibasic acid used will be in substantially equimolecular proportion.

While any of the fiber-forming polyamides may be used for the production or the yarns and threads contemplated herein, applicant prefers polyhexamethylene adipamide. However, nylon yarns and threads prepared from polyhexamethylene sebacamide, polydecamethylene sebacamlde. G-aminocaproic acid polymer and other polyamides and interpolyamides such as are disclosed in U. S. Patents Nos. 2,130,948, 2,214,405, 2,298,868 and 2,071,253 may also be treated in accordance with this invention. The invention includes polycarbonamide yarns and threads, e. g. polyureas such as polydecamethylene urea; the product prepared by reacting monoaminomonohydric alcohols with dibasic carboxylic acids, e. g. that prepared by reacting sebacic acid and monoethanolamine may also be used as well as polysulfonamides (U. S. Patents Nos. 2,321,890 and 2,321,891), e. g. the polysulfonamide derived from decamethylene-diamine and m-benzenedisulfonyl chloride; polyurethanes and polythiourethanes (U. S. Patent No. 2,284,637), for example the polymer derived from decamethylene-diisocyahate and decamethylene glycol; poiythionamides (U. S. Patent No. 2,201,172), e. g. polydecamethylene thiourea; and polyhydrazides, e. g. that derived from hydrazine and sebacic acid may be used.

The elongations referred to herein are determined by exposing the yams or sewing threads at 78 F. and at a relativehumidity of 72% until the yarn or thread is in moisture equilibrium with the atmosphere, a tolerance of :29; being permitted in relative humidity and of :29 permitted in temperature. The elongations referred to are breaking elongations. All yarns and sewing threads are tested for elongation on a Suter single strand testing machine of suitable capacity, the distance between the clamps being 18 inches. The speed of the pulling clamp of the said Suter machine which is a pendulum type testing machine is 12 inches per minute. The specimens for strength determination are drawn from the side of the package instead oi over the top to avoid a change in twist. Specimens in which the thread breaks at the jaw are rejected. Tensile strength is likewise measured on this machine, being expressed in rams per denier obtained by dividing the breaking strength by the denier of the yarn being tested.

It will be understood that these sewing threads may be delustered, dyed or otherwise colored and that they may contain an agent to improve their light stability, 01 an agent may be added for some other similar purpose. It will be understood too that the sewing threads will ordinarily be treated with a yarn finish as is well known.

One of the unexpected results of this invention arises in connection with the ironing of garments sewn withthese threads. It has been found that while the ironing temperature may be in excess of the melting point of the untreated yarn, the treated yarn does not have a sharp thread made by twisting methyleneadipamide yarns having elongations melting point, but rather a gradual softening Point and that it is sufficiently high to resist the rigors oi ironing well.

The invention has been described in terms of sewing thread. It will be obvious that these threads and yarns will find utility in other connections and the invention contemplates these as well.

Any departure from the procedure described herein which conforms to the principles of the invention is intended to be included within the scope of the claims.

I claim:

1. A process which comprises conditioning a thread made by twisting together at least two oriented yarns prepared from synthetic linear polyamides, said conditioning being so conducted at temperatures below 100 C. to impregnate said thread with from 0.2% to 2.0% formaldehyde based on the weight of said thread and to reduce the moisture content of said thread so that the said content is at most 5%; hot stretching resultant conditioned thread 10% to 30% at a temperature of 190 C. to 215 0.; and cooling said conditioned thread at least maximum stretching temperature above 0' C. while maintainin said thread in its stretched position.

2. A process which comprises conditioning a thread made by twisting together at least two oriented polyhexamethyleneadipamide yarns, said conditioning being so conducted at temperatures below 100 C. to impregnate said thread with from 0.2% to 2.0% formaldehyde based on the weight of said thread and to reduce the moisture content of said thread so that the said content'is at most 5%; hot stretching resultant conditioned thread 10% to 30% at a temperature of 190 C. to 215 0.; and cooling said conditioned thread at least 5% below the maximum stretching temperature above 0 C. while maintaining said thread in its stretched position.

3. A process which comprises conditioning a at least two polyhexanot exceeding 30%, said conditioning being so conducted at temperatures below 100 C. to impregnate said thread with from 0.2% to 2.0% formaldehyde based on the weight of said thread and to reduce the moisture content of said thread so that the said content is at most 5%; stretching the thread 10% to 30% at a temperature of C. to 215 C., and cooling said conditioned thread at least 5% below the maximum stretching temperature above 0 C. while maintaining said thread in its stretched position.

.rosnpn Emma wamz.

nnrsnnncns CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 5% below the Number Name Date 2,177,637 Coifman Oct. 31, 1939 2,275,008 Coiiman Mar. 3, 1942 2,288,279 Hopfl et al June 30, 1942 2,360,352 Lodge Oct. 17, 1944 2,385,403 Conaway Sept. 25, 1945 2,389,655 Wende Nov. 27, 1945 FOREIGN PATENTS Number Country Date 419,826 Great Britain; Nov. 19, 1934 565,066 Great Britain Oct. 25, 1944 

